Bumpology: Is my baby making me forgetful?

Bumpology is our weekly column on the science behind pregnancy, written by our reporter whose own bump is growing larger by the day

Days until birth: 89

Waist size: 91.5 centimetres (36 inches)

Additional note: Finding it increasingly difficult to get comfortable at night and baby's kicks are getting stronger. Perhaps this also explains my vacancy.

The first indication that something might be up came when I caught myself asking my friend how she was feeling twice in the space of 30 seconds. Then I got into my car and couldn't find my keys, until a helpful passer-by pointed out that they were sitting in the lock outside.

Since then, I've caught myself losing track of what I'm saying mid-sentence, and walking upstairs only to realise that I have no recollection of what I've gone up there for. It seems that "mumnesia", the forgetfulness that is said to beset pregnant women, may finally be taking hold.

But a new study casts fresh light on exactly how pregnancy might interfere with memory in women, as well as exploring how long the effects last. It is also one of the largest studies looking into pregnancy and memory to have been conducted so far.

Laura Glynn at the University of California, Irvine, asked 254 pregnant women to perform a series of memory tests at different stages of their pregnancy, as well as 12 to 14 weeks after the birth. She also measured levels of the hormones oestrogen and cortisol in their blood, and repeated these tests on 48 non-pregnant women.

Lost words

Glynn found that after around 29 weeks of pregnancy, pregnant women did start to perform worse than non-pregnant women – but only when it came to remembering pairs of words (verbal memory). This effect also persisted after birth.

What's more, the decline in verbal memory seemed to be related to hormone levels: women who experienced high levels of oestrogen during early pregnancy and lower levels of the stress hormone cortisol throughout pregnancy experienced the most marked fall in verbal memory performance.

"These hormones have been shown in the non-pregnant state to be intimately involved in learning and memory, Glynn says. "In particular, the hippocampus – a part of the brain that is involved in the verbal recall memory task – is very sensitive to changes in oestrogen and cortisol."

Preparing for motherhood

Both these hormones are also thought to contribute to the development of maternal behaviours, with high oestrogen in particular having been linked to increased feelings of attachment to children after birth. In other words, memory impairment might be a casualty of other changes in the brain that are preparing women for motherhood.

"The message I'd like women to take away is that the changes that are occurring may make you a better mother," says Glynn.

The discovery that these hormones also predict memory performance after birth may support the idea that persisting "brain fog" after birth is not purely the result of sleep deprivation, Glynn says.

One remaining question is whether these changes persist for longer than 12 to 14 weeks after the birth of a baby. Another is whether women's brains benefit in other ways from the changes that take place during pregnancy.

Although verbal memory might take a hit, "it is possible that when faced with different tasks, for example, those more directly related to the care of offspring such as multitasking, performance under stress or sensitivity to infant cues, mothers might exhibit enhanced performance," Glynn says.

Studies of rodents have suggested that pregnancy results in greater resilience to stress. And Rebecca Pearson and her colleagues at the University of Bristol in the UK recently found that women's ability to read faces expressing fear, anger and disgust also increases during pregnancy – possibly priming women to be hyper-vigilant once they become mothers.

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